1. Field of the Invention
The present invention relates to a variable propeller for a boat in which a propeller boss is fitted and connected to a propeller shaft, and a plurality of propeller blades are rotatably mounted to the propeller boss through a plurality of blade shafts disposed to surround an axis of the propeller boss and along the axis thereof so as to effectively vary a propeller-diameter.
2. Description of the Prior Art
Such a variable propeller as described above has been already known as disclosed, for example, in U.S. Pat. No. 3,565,544. The variable propeller disclosed in the above mentioned patent has independent propeller blades and is rotated so as to vary the propeller-diameter by the balance between the centrifugal force exerting thereon and the drag of water. In the above proposal, however, due to partial conditional changes during cruising, for example, a partial cavitation caused during cruising in shallows and during a sudden turning movement, opening angles of flange blades become uneven or the opening angles are repetitively increased or decreased to impair the smoothness of rotation of the propeller.
The present invention has been achieved in view of the above circumstances, and it is an object of the present invention to provide a variable propeller which can always equally control all the propeller blades while making use of the centrifugal force despite the partial conditional changes during cruising to precisely adjust the propeller-diameter.